Image copyrightAFPImage caption
Smoke billowed from the factory after the explosion

Ciudad Juarez is in the state of Chihuahua on the border with the US state of Texas.

Factories such as the one affected, known as maquiladoras, are located in a free trade zone between the United States and Mexico.

They are estimated to employ more than one million Mexicans.

The BBC's Will Grant in Mexico City says maquiladoras are often criticised by labour rights groups for their low wages and poor working conditions, as they try to compete with China to manufacture cheap goods for the US market.